Midterm 2 - CT, MRI, Scintigraphy, Ultrasonography Flashcards Preview

Radiation Physics And Safety > Midterm 2 - CT, MRI, Scintigraphy, Ultrasonography > Flashcards

Flashcards in Midterm 2 - CT, MRI, Scintigraphy, Ultrasonography Deck (54)
Loading flashcards...
1

CT was invented by who (2) in what year?

Hounsfield and McLeod
1973

2

Modern scanners have multiple detector arrays that are stationary around what degree of the patient?

360 degrees: tube rotates around patient

3

The CT tube rotates around patient in the ___ plane

Axial

4

Helical CT scanners create a ______ acquisition of data

Spiral

5

Multi-slice scanners create data in thin slices, referred to as

Volumetric acquisition

This means 1) there are no gaps in acquisition of data and 2) when data is reformatted, the quality is as good as axial data.

6

What are small squares of CT data that make up the image we see on axial orientation scans?

Pixels — picture elements

7

What are comprised of pixel element PLUS depth of box?

Voxels — volume elements

8

What kind of scanner can produce isotopic voxel?

Helical CT

9

What is a voxel that has the same depth, width and height?

Isotopic voxel

In other words, the resolution of the data is the same no matter which plane you choose to see — the voxel and pixel elements have the same dimensions.

10

Reformatting allows views of data from:

Sagittal, coronal or 3-D

11

What are used to describe the shade of grey that a tissue presents on the scale on CT?

Hounsfield units (HU)

12

HU scale ranges from

-1000 to 3072 HU

13

Only ___ (#) HU can be assigned per pixel/voxel

1

14

HU translate to grey scale. +1000 is going to be [lighter/darker] -1000 [lighter/darker]

+1000 = lighter e.g. bone
-1000 = darker e.g. air

15

What is the process of emphasizing certain ranges in the HU scale? E.g. if we want to see more bone e.g. higher value end of the HU scale OR if we want to see more soft tissue

Windowing

Soft tissue windows allow better viewing of the low HU end of the scale: soft tissues.

Bone windows emphasize the higher value end of HU scale: cortical and medullary bone.

16

What is -1000 HU?

Air

17

What is 0 HU?

Water

18

What is +400 HU?

Cancellous bone

19

What is +700 to +2000 HU

Cortical bone

20

What is +2500 to +3000 HU

Metal

21

When the CT detector cannot distinguish between different tissues because they are in the same pixel, its called

Partial Volume Effect

(Machine has to decide if it will make the Pixel black or white.)

22

What technology uses a magnetic field?

MRI

23

In MRI, echo time (TE) and repetition time (TR) allow what?

Creation of sequences known as T1 and T2

24

In MRI, what is brightest for T1-weighted image? What is not bright?

Brightest: Fat
Not brightest: Water and fluid

Note: opposite is true for T2

25

In MRI, what the high signals/low signals in T2-weighted images

Bright = water & fluid
Not bright = fat

Basically, the less free protons, the lower signals
Compact tendon = low signal

26

A T-2 weighted sequence can be converted to a _____ sequence

FLAIR, Fluid Attenuated Inversion Recovery

27

What kind of image suppresses fat signal in MRI to make it appear black so that you can see tissue and fluid better?

STIR (short tau inversion recovery)

28

Overall, T1 vs T2 vs fluid sensitive studies (FLAIR, STIR) (what are they good for)

T1 = evaluate anatomy
T2 = find pathology
FLAIR, STIR good for pathology and edematous/watery tissues

29

Batteries e.g. cardiac pacemakers, insulin or infusion pumps; metals e.g. shrapnel from accidents or some high metallic tattoos; patients who can’t stay still because of seizures... these are contraindications for what procedure?

MRI

30

Looking at an MRI, the fat is bright. What weight of MRI is it?

T1